Add/Transfer one object's weight painted vertex groups to different object (identical mesh)?
There may be a more streamlined way.
The nose rig didn't change between the eyes-rig and lips-rig face objects, so I duplicated them both -&gt; deleted the nonfunctional halves of each mesh at the nose bridge -&gt; merged (Ctrl+J) the functional halves. I also merged the same-loop/XYZ-coords edge loops  (Merge by Distance) and cleared sharp edges to resolve a subtle but obvious shading issue. Here, Shift+D and Alt+D didn't seem to differ as a duplication method.